Testis development and testosterone secretion in captive European ground squirrels before, during, and after hibernation

Abstract

In some hibernating species, an extended euthermic period before spring emergence has been reported during which testicular maturation occurred. In this study, we investigated whether male European ground squirrels Spermophilus citellus (Linnaeus, 1766) develop scrotal testes before or after the termination of hibernation. The course of testis development and testosterone concentrations were examined in young-of-year male ground squirrels (n = 4) before, during, and after their first hibernation. In the environmental chamber, all animals showed regular hibernation patterns with decreasing torpor bout lengths prior to the end of hibernation. Four weeks before hibernation ended, testosterone levels were elevated during spontaneous arousals. Testosterone concentrations peaked during the first 2 months post heterothermy and decreased thereafter. In 2 experimental males, testes descended from the inguinal region into the scrotum shortly before the end of heterothermy. The state of testis development and testosterone secretion corresponded to that found in semi-free-living males at spring emergence. Testis size increased in active animals to maximum widths during weeks 3 and 4 post heterothermy. Scrotal skin pigmentation was absent until heterothermy ended and developed during the first month thereafter. The data suggest that male S. citellus do not need a pre-emergence euthermic period for reproductive development.